Over the past 25 years our research efforts have focused upon the cortico-cortical connections of the rhesus monkey cerebral cortex. The results of these investigations have given us considerable insight into the connections of the primary sensory, sensory association, and limbic cortices as well as the interhemispheric connections of many of these areas. More recently we have investigated the intrinsic connections within the primary sensory and sensory association areas of the visual and somatosensory systems. These investigations have focused upon the detailed cortical organization within these areas including the exact type of neuron that gives rise to each local circuit connection, the precise laminar pattern of termination for each connection, and most recently, the relationship of these cortical connections to subcortical afferents. In this grant application we propose to extend these more detailed investigations of cortical organization to the cortices of the primary auditory area, the cingulate gyrus, and the parahippocampal gyrus. Specifically we plan to investigate the precise manner in which callosal, thalamic and association afferents terminate within the primary auditory cortex. We will extend this investigation to the ultra-structural level by using the combined Golgi-electron microscopic technique to identify the exact neuron and synaptic termination for the callosal afferents. In the parahippocampal and cingulate areas we will investigate the exact termination and neuron of origin for both subcortical and intrinsic afferents within cytoarchitecturally defined subdivisions of these heterogeneous cortices as well as the efferents, both cortical and subcortical, that originate from each of these subdivisions. Finally, in the cingulate gyrus we will begin to investigate some of the histochemical properties of these connections by identifying neurons with opiate receptor binding in order to correlate this with the termination pattern of the various afferents.